zink: handle isign alu in ntv

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5562>
diff --git a/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c b/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
index 40a0b26..00410a7 100644
--- a/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
+++ b/src/gallium/drivers/zink/nir_to_spirv/nir_to_spirv.c
@@ -1239,6 +1239,7 @@
    BUILTIN_UNOP(nir_op_ftrunc, GLSLstd450Trunc)
    BUILTIN_UNOP(nir_op_fround_even, GLSLstd450RoundEven)
    BUILTIN_UNOP(nir_op_fsign, GLSLstd450FSign)
+   BUILTIN_UNOP(nir_op_isign, GLSLstd450SSign)
    BUILTIN_UNOP(nir_op_fsin, GLSLstd450Sin)
    BUILTIN_UNOP(nir_op_fcos, GLSLstd450Cos)
 #undef BUILTIN_UNOP